Method and apparatus for register mark identification

ABSTRACT

A Color Register Control system used to maintain close registration between colors printed on a surface by various printing cylinders. The control system acquires an image of a cluster of register marks printed by various printing cylinders. The register mark is a geometrically unique mark, The mark cluster is acquired by the camera and each mark pattern is identified by checking shape of individual marks. Resulting location of a mark is used to compute and correct registration errors. The image is analyzed to identify marks printed by various printing cylinders. Register error is determined by computing the lateral and circumferential distance between marks printed by a print cylinder and a master print cylinder. Any error detected in this process is corrected by activating correction motors typically stepper motors, on print cylinders. The control utilizes a commercially available IBM-PC compatible computer, which can accept additional boards in the expansion slots for indicated purposes.

This application claims the benefit of provisional application Ser. No.60/057,320, filed Sep. 2, 1997

FIELD OF THE INVENTION

Apparatus and method particularly suitable for use with closed loopcolor to color registration system of a web printing apparatus includinga unique graphical user interface and register mark identificationscheme.

BACKGROUND OF THE INVENTION

It is known in the prior art to search out register mark patterns whichreoccur.

Procedures useful in accomplishing this involve the identification ofrepetitive color marks as they appear in this recurring format.Techniques to date include determining and correlating position andcolor information for recurring elements in a repetitive pattern.

One such scheme searches out the existence of substantially identicaldot pairs in each pattern and then their reoccurrence in subsequentpatterns.

Further in prior art system interface schemes, technology has onlyadvanced to the point of permitting the inputting of key parameters andrelated changes through the combined coordination of visual display andkeyboard entries.

SUMMARY OF THE INVENTION

The function of a Color Register Control system on a printing press isto maintain close registration between colors printed on a surface byvarious printing cylinders. The control acquires an image of a clusterof register marks printed by various printing cylinders. The registermark is a geometrically unique mark. The mark cluster is acquired by thecamera and each mark pattern is identified by checking shape ofindividual marks. Resulting location of a mark is used to compute andcorrect registration errors. The image is analyzed to identify marksprinted by various printing cylinders. Register error is determined bycomputing the lateral and circumferential distance between marks printedby a print cylinder and a master print cylinder. Any error detected inthis process is corrected by activating correction motors, typicallystepper motors, on print cylinders.

The control utilizes a commercially available IBM-PC compatiblecomputer, which can accept additional boards in the expansion slots.

A commercially available touch-screen monitor is utilized in a uniqueway for operator interface so as to accept operator commands and todisplay results utilizing only the touch-screen monitor.

BRIEF DESCRIPTION OF DRAWINGS:

Following are the details of the attached figures.

FIG. 1 is an illustration of typical mark pattern on one surface. Eachmark is of unique geometrical shape. Each mark is printed by a separateprinting cylinder. All marks are shown in register.

FIG. 1A is an illustration of typical mark pattern on one surface, shownwith a registration error (#86).

FIG. 2 is a block diagram giving details about general procedure forcalculating and correcting register error.

FIG. 2A is a block diagram giving details about qualifying blobs(block106 in FIG. 2) in an acquired image as possible register marks.

FIG. 2B is a block diagram giving details about identifying marks(block108 in FIG. 2) to match with the pre-defined pattern of mark coming froma print cylinder.

FIG. 2C is a block diagram giving details about identifying lobes(block306 in FIG. 2B) around a qualified mark.

FIG. 2D is a block diagram giving details about filtering duplicatemarks(block 110 in FIG. 2) based on region of interest decided by thelocation of a master mark.

FIG. 3A is an illustration of the apparatus giving details about the webmovement and camera module, camera module moving mechanism andassociated mechanical components.

FIG. 3B is a block diagram giving details of web movement direction andthe position of two camera modules in the system to scan two surfaces ofa web.

FIG. 4 is a functional block diagram depicting the general arrangementof certain components of the present control system.

FIG. 5 and FIGS. 5A through 5K depict various screen displaysencountered in the graphical user interface portion of the presentinvention (there is no FIG. 5I).

FIG. 6 is a perspective view of the control console used in theimplementation of the system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Typical printing process on a printing press utilizes printing cylindersto print an image on a surface of web. Print cylinders are driven withdrive shaft. Since this is a repetitive process, the register markprinted by a printing cylinder remains reasonably at the same locationfrom one impression to other impression. Each print cylinder prints ageometrically distinct mark on one surface as illustrated in FIG. 1(80-94). All register marks on a web surface form a cluster of registermarks. There can be multiple clusters on a web surface at differentlocations.

The touch screen operator interface allows the operator to interact withthe control for specifying various operating parameters for the process.Depending on the printed surface requirements, an operator can enable ordisable a complete web surface in the control. Operating buttonsspecific to the disabled web are not displayed on the control. Operatorcan also specify the number of printing cylinders active in the totalprinting system. Additional printing cylinders not being utilized arenot displayed on the operator interface with active print cylindersspaced out on the control panel for ease of operation. Operator can alsodefine multiple printing cylinder as non-printing cylinders, which arestill displayed on the operator interface but no further operations areallowed for those printing cylinders.

From all print cylinders printing on a web surface, operator can specifya print cylinder as a master print cylinder. During automaticoperations, this cylinder is not moved and all register errors for otherprint cylinders printing on this surface are calculated with masterprint cylinder register mark location as the reference location.

With the touch screen interface, operator can also re-assign any printcylinder to any web surface, indicating that the selected print cylinderis printing on the selected web surface.

A register mark cluster consists of multiple mark patterns printed on aweb surface. Each register mark is geometrically of unique shape,printed by a specific print cylinder. During set up, operator alsospecifies the pattern of mark printed by a specific print cylinder.

The Color Register Control console 10 (see FIG. 6) utilizes a 17″Capacitive Touch Screen Monitor(12), commercially available from PixelTouch Company. A capacitive touch screen arrangement utilizes a glassoverlay in front of the CRT of the monitor. The glass overlay is coatedwith an electrically conductive transparent coating. The overlay isconnected to a controller card, which determines the position where thescreen is touched. The touched coordinate information is transmitted tothe personal computer operating system, like Windows 95, through serialcommunication port. A mouse emulating software drivers are provided bythe touch screen manufacturer to emulate screen touch as mouse movementand clicks. The display area utilizes high resolution, 1024 pixel×768pixel, to display all icons and information on the screen.

The graphical user interface for the control is designed utilizing acommercially available software package such as Visual Basic byMicrosoft. This software is used to create graphical user interfaceelements like Windows buttons and panels.

The main control panel (#800) of the control, displayed in FIG. 5. isdivided into various functional groups, each consisting of one or morecomponents. The group on the top of the screen (#802) displays thecurrent job name (#804), printing press speed in Impressions Per Hourand in Feet per minute (#806), current date and time (#808). The companylogo (#810) on the top left corner of the screen is also utilized toaccess parameters for the control through password protected access. Itwould be used to change operating parameters of the system, e.g., numberof print cylinders, activation speed, motor speed and active surfaces.

The Press Status Window group (#820) displays the status of all printingcylinders (#822A and #822B) in the system. Information in this window isupdated every 1 second. All print cylinders are circles filled withcolor assigned by the control operator. A white color of a cylinder(e.g. #801) indicates that the cylinder is a non printing cylinder. Itcannot be selected for any further operations until a non-white color isassigned to the print cylinder.

A cylinder can be selected for a desired operation by touching thecylinder or the rectangular gray area (#803) around the cylinder.Cylinder selection is indicated by flashing hatched lines (#832) in thefilled area of the circle. Selection of a cylinder can be canceled byagain selecting the selected cylinder.

Next to each cylinder, a cylinder status circle (#824) is included toemulate a status light. The fill color of the status circle changesaccording to the status of the print cylinder. When the cylinder statusis MANUAL, the status circle is transparent. When switched to AUTO mode,and a corresponding register mark is found, the fill color of the statuscircle is green. If the cylinder is in AUTO mode but a correspondingregister mark is not identified, the fill color of the status circle isred. If the cylinder is switched to a Manual Override mode, the statuscircle is filled with blinking yellow color.

Next to the cylinder area, a dark gray background window (#826) isprovided to display Circumferential Register error/correction andanother dark gray area (#828) is provided to display Lateral Registererror/correction. These areas are divided in two parts. The biggerportion (e.g. #805) displays the amount of error; and the smallerportion (e.g. #807) displays the direction of register motor movement.Error and direction information are displayed until the time when theregister motor is making correction moves. A white line (#830) betweenthe two cylinders (#822A and #822B) indicates the substrate beingprinted. Top and bottom printing cylinder with the status circle andregister error display areas are included in a vertical rectangularframe to represent a perfecting printing press unit (#834). Completeprinting press can be represented by up to 10 printing press units witha total of 20 printing cylinders. A number (#809) is assigned to eachprinting unit for ease of identification. A complete printing press unitcan be selected by touching a rectangular area around the Press UnitNumber. The selected printing press unit is displayed with flashing cyancolor. The printing press unit selection can be canceled by againselecting the selected printing press unit.

Different information about the print cylinders is displayed in theregister display area, based on selected control function.

A Control Button Window group (#840) is provided with a group of controlbuttons used to access different functions of the control. It consistsof buttons to access a job file management window (#880), a job editwindow (#882), a statistics window (#884). a view window (#886), a setupwindow (#888) and a help window (a further help button is provided ineach window to access context sensitive help). Buttons are enabled anddisabled in this window depending on the type of functions desired to beaccessed by the operator.

A Panic Button (#850) is provided and it is active and available on thescreen at all times except when accessing the help information.

A Main Message Window (#860) displays system messages for the operator.The control periodically displays any error messages or status messagesin this window.

A Variable Window (#870) displays additional windows depending on theoperator selected functions as described hereinafter.

During normal running, this Variable Window displays a keypad withoperating controls (#900) as illustrated in FIG. 5A. The window displaysnumeric keys (#902) from 0 to 9 in a typical format similar to atelephone. In addition to the numbers, a Clear key (#904) is provided.Operator touches the clear key to clear any numeric value input. Anynumeric value input by the operator by touching numeric keys is alsodisplayed in the keypad display area (#906). Four Movement DirectionKeys (#908) are provided to specify the direction of the movement forthe register motors. To move a print cylinder, the operator firstselects the print cylinder in the Print Status Window group (#820) bytouching it; followed by touching keys (#902) required to enter theamount of movement; followed by touching the direction key correspondingto one of the four desired directions-the “man silhouette” and the“gear” are used for lateral direction changes, while the “+” and “−”cover circumferential corrections.

In addition to these keys, the Keypad also consists of Surface SelectionKey group (#910), MANUAL key (#912), AUTO key (#914) and MotorEnable/Disable Key (#916). The Surface Selection Key group may displayfour keys to indicate up to four surfaces of two webs identified as Aand B webs (#901 and #903). The arrow icon on these keys indicate thedirection of printing on the web.

Color of the icons in respective areas (#905) change with the status ofthe surface. When surface is in MANUAL, the respective area is paintedred. When surface is in AUTO mode, the area is painted green. Whenmotors on a surface are disabled, the areas are painted yellow.

When control is searching for the register mark cluster on a surface,the icon on the corresponding surface selection key group moves up anddown in bouncing motion, indicating the control is in a search mode forthat specific surface.

Surfaces can be switched to MANUAL mode by selecting required surfacesand then touching the MANUAL key (#912). Surfaces can be locked in AUTOmode by selecting required surfaces and then touching the AUTO key(#914). Once locked in AUTO, individual print cylinders can be switchedto Manual Override mode by selecting a locked cylinder and then touchingthe MANUAL key. While locking surfaces in AUTO mode, operator has threechoices, indicated with a pop up window with three buttons. The firstbutton is captioned “IDEAL”. If an operator selects this button, thecontrol searches for all register marks in a cluster and onceidentified, it brings the relation between the marks to the ideal value.The second button is captioned “CURRENT”. If an operator selects thisbutton, the control searches for all register marks in a cluster andonce identified, it maintains the current found position of the registermarks. The third button is captioned “LAST”. If an operator selects thisbutton, the control searches for all register marks in a cluster andonce identified, the control brings the register mark to therelationship of the last job run.

Touching the “FILE” key (#880) opens a File utilities window (#1000) inthe Variable Window Area, illustrated in FIG. 5B. This window consistsof following keys:

If the operator touches “NEW” key (#1002), the control loads a DEFAULTjob in the memory. If the operator touches “SAVE” key (#1004), currentjob is saved in back in the same file. If the operator touches “SAVE AS”key (#1006), a keyboard window pops up. Operator can input new name ofthe job file by touching appropriate alpha-numeric labeled keys todefine the new file name. If a job file already exists with the samename, the control displays a confirmation pop up window. If operatoraccepts, current job file details are stored in the existing file. Ifoperator does not accept to overwrite existing job file, the operationis aborted. If the operator touches “ERASE” key (#1006), file selectedin the file list window (#1008) is erased from the memory. Operator canselect file from the file list window (#1008) by touching the file namein the window or by using the scroll bars (#1010) to move the selection.Before erasing the file from the memory, the control displays aconfirmation pop up window. If operator accepts, selected file is erasedfrom the memory. If operator does not accept, file erase operation isaborted. If operator touches “OPEN” key, the file selected in the filelist window (# 1008) is loaded in the memory and current file name isupdated. A “HELP” key (#1014) is provided for accessing contextsensitive help on FILE operations. A “RETURN” key (#1016) is provided toreturn back to the MAIN screen (FIG. 5).

Touching the “STATISTICS” key (#884) on MAIN screen opens a statisticalwindow (#1100) in the Variable Window Area, illustrated in FIG. 5C. Thiswindow consists of a graph window (#1102) giving sample number on thehorizontal axis and error on the vertical axis. To view statisticalresults for the last sample of a pre-defined size, the operator firstselects a print cylinder by touching the print cylinder in the PressStatus Window (#820) and then touches the OPERATOR/GEAR” side key(#1104) or the “ADVANCE/RETARD” key (#1106). The graph window is updatedto see the last sample results. Also, the statistical window displaysextreme error (#1108) in last sample, mean error (#1110) in last sampleand standard deviation (#1112) for the last sample. This result is veryuseful to the operator in fine tuning the press parameters to optimizethe performance since it allows the operator to objectively compare thequality produced with two different settings and choose the best settingfor the job. A “HELP” key (#1114) is provided to get immediate contextsensitive help on Statistical Window and interpretation of results. A“RETURN” key (#1116) is provided to return back to the MAIN screen.

Touching the “VIEW” key (#886) opens a camera view window (#1200) inVariable Window, as illustrated in FIG. 5D. This window consists of aSurface Selection Key group (#1202) as explained earlier. It alsoconsists of an image window (#1204) to display the exact image grabbedby the camera, in a smaller scale. The image is refreshed once every 1second. A group of four keys (#1210) is provided to manually move theimage assembly in appropriate direction for acquiring an image otherthan the operator specified location. A “HELP” key (#1206) is providedto get immediate context sensitive help on View Window. A “RETURN” key(#1208) is provided to return back to the MAIN screen.

Touching the “JOB EDIT” key (#882) opens the first of the severalwindows (FIGS. 5E to 5K) in the Variable Window location. Each window inthis set of windows has a “HELP” key (e.g. #1302) for context sensitivehelp for that specific window. Each window in this set is also equippedwith navigational keys. The “PREVIOUS” key (#1304) closes current windowand opens a previous window. The “NEXT” key (#1306) opens next windowand the “RETURN” key (#1308) returns control to the MAIN screen. An“UNDO” key (#1310) is provided on each window to discard all changesmade during this setup and restore the settings to the values just priorto entering the Job Edit menus.

The first window opened under the “JOB EDIT” function is the “ColorAssignment” window (#1300) as illustrated in FIG. 5E. This windowconsists of several keys with a captioned circle filled with differentcolors (#1312). One larger key is captioned with a white circle (#1314).To assign a specific identifying color to a print cylinder, the operatorselects a print cylinder from the Press Status Window group (#820) bytouching the cylinder and then touching the appropriate color key in theColor Assignment window. Assigning the color white to a cylinderindicates that the cylinder is non printing. A non-printing cylindercannot be selected from any other window except from the ColorAssignment window. This feature prevents the operator from erroneouslyselecting a print cylinder and moving it.

The second window opened is the “Surface Assignment” window (#1400) asillustrated in FIG. 5F. This window consists of Surface Selection Keyset (#1402). Along with these keys, a surface Enable/Disable key (#1404)is provided which changes the state of the associated surface to Enabledor Disabled. Also, with each surface selection key, a master printcylinder select key (#1406) is provided. In order to define a printcylinder on a surface as a master print cylinder, the operator selectsthe required print cylinder and then touches the master print cylinderselect key (#1406) corresponding to the surface on which the selectedprint cylinder is printing. The print cylinder once selected as a masterprint cylinder, adopts the color within the white ring appearance as,for example, #811 in FIG. 5.

This window is also used to re-assign a different surface to a printcylinder. To reassign a print cylinder to a different surface, theoperator selects the required print cylinder followed by touching thesurface selection key (#1402) on the window. This feature is very usefulin setting up jobs for multiple webs and multiple web paths.

The third window opened is the “Region Assignment” window (#1500) asillustrated in FIG. 5G. This window consists of Surface Selection Keyset (#1502). The operator touches appropriate surface key for which theregion assignment is required. A Region Definition Window (#1504)consists of different lobed shapes of register mark and their relativeposition. To change a region assignment for a print cylinder, theoperator selects a print cylinder and then touches the required markpattern displayed in the Region Definition Window. The register markschematic in the window is filled with the color of the print cylinderto which it is assigned. This procedure establishes link betweendifferent shapes and the print cylinder printing that specific shape.

The fourth window opened is the “Target Assignment” window (#1600) asillustrated in FIG. 5H. This window consists of Surface Selection Keyset (#1602). The operator touches appropriate surface key for which thetarget assignment is required. Each surface in the system can have up toeight target locations specified with the Target Number Keys (#1604).The Master Target followed by the imaging assembly is displayed by thetarget number captioned enclosed in braces (#1606). The operator selectsthe target by touching appropriate target numbered key (#1604).Circumferential location of the selected target is displayed in window(#1608). Lateral location of the selected target is displayed in window(#1610). Value of Circumferential and lateral location can be changed bytouching the scroll bars adjacent to the corresponding value windows.Impression Window (#1612) represents one press repeat length of the web.Approximate location of the selected target is displayed by a redcolored filled square mark (#1614) in the Impression Window (#1612).Orientation of the selected register mark cluster is displayed by theicon of the Orientation Button (#1616). This button works like a toggle.To change the orientation of the selected register mark cluster,operator touches this button. Preset Buttons a-f (#1618) are providedwith pre-defined locations and orientation of the register markclusters. To change location and orientation of the selected registermark cluster, operator simply touches appropriate Preset Buttons. Afterall editing is done for each surface, operator touches the “CONFIRM” key(#1620) to confirm the changes made to the register mark properties.

The fifth window is the “Surface Properties” window (#1700) asillustrated in FIG. 5J. This window consists of Surface Selection Keyset (#1702). The operator touches appropriate surface key for which theSurface Properties definition is required. Required property is selectedby touching one of the property descriptions listed in the Property ListWindow (#1704), or by touching the adjacent scroll bar. Current value ofthe property is displayed in window (#1706) with minimum possible valueof the selected property displayed in window (#1708) and maximumpossible value of the selected property displayed in window (#1710).Current value of the selected property can be changed with a scroll barbetween minimum and maximum value windows.

The sixth window is the “Cylinder Properties” window (#1800) asillustrated in FIG. 5K. The operator selects the print cylinder forwhich the Print Cylinder Properties definition is required. Requiredproperty is selected by touching the property description in PropertyList Window (#1804), or by touching the adjacent scroll bar. Currentvalue of the property is displayed in window (#1806) with minimumpossible value of the selected property displayed in window (#1808) andmaximum possible value of the selected property displayed in window(#1810). Current value of the selected property can be changed with ascroll bar between minimum and maximum value windows.

Touching the “SETUP” key (#888) in the Control Button Window group(#840) opens a Maintenance and Setup window. This window consists ofseveral key groups.

The first key group is for cylinder centering in lateral andCircumferential direction. In order to center the cylinders betweencorresponding limits, the operator selects the cylinders to be centeredby touching the cylinders in the Press Status Window, followed bytouching the key indicating Centering-Lateral orCentering-Circumferential. The selected cylinders start moving to oneside until they detect a limit condition. Then the control startscounting time and it moves the cylinders in opposite direction untilsecond limit is detected. The time lapse from first limit to secondlimit is calculated. Now, the control moves the cylinder towards thefirst limit for half the time lapsed for travel between first and secondlimit. This process is simultaneously performed for all selected printcylinders.

A second key group is used for calibrating the camera aperture forappropriate exposure. When this key is touched, all imaging modules forall surfaces start firing randomly. If a stationary image is pasted atthe target location in front of the imaging module camera and press isrun in slow run mode, the operator can watch the quality of the imagegrabbed and calibrate the camera aperture for required exposure. A helpkey is provided to get immediate context sensitive help on Setup Window.A RETURN key is provided to return back to the main menu.

The description now is directed to the unique method and system of thepresent invention for register mark identification. A typical registermark cluster is displayed in FIG. 1 (80-94), in which, each mark from#80 to #94 are printed by a different print cylinder. The mark clustersmay be printed along the length or across the width of the web surface.Multiple mark cluster can be present on a printed surface. Each markcluster carries a lateral position value circumferential position valueand orientation value. During setup of machine, the operator specifiesthe mark cluster to be identified and followed. As soon as the operatorspecifies the mark cluster to be followed, the control pre-positions thecamera module to save time and paper waste.

The control system utilizes an encoder (#714, see FIG. 4), driven fromthe drive shaft driving the print cylinder, to continuously monitorposition of the drive shaft, and thus monitor the position of the printcylinder. An electronic Encoder Control Board is inserted in one of theexpansion slots of the CPU. The function of this board is tocontinuously monitor the counts coming from the encoder. Up to fourdistinct counters are provided on a board for four printed surfaces.When the count from encoder matches a preset value for a specificsurface, specified by the operator during set up procedure, the EncoderControl Board outputs a trigger signal of specific time duration andcontinues counting. For each surface to be monitored, one commerciallyavailable Frame Grabber board is also inserted in the CPU expansionslot. The function of this board is to acquire and store the imagereceived from a charge coupled device (CCD) camera. Each surface ismonitored by a commercially available CCD Camera such as Hitachi'sKP-M1. The camera in this system is left free running and it is alwayson. Since the web to be inspected is moving at a high speed, acommercially available high speed high intensity strobe is fired tofreeze the motion of the web. The trigger signal from the encoder boardfires a strobe. The Frame Grabber acquires and stores the next completeframe image from the camera.

The acquired image is then analyzed by the personal computer CPU, toidentify the register marks in the image, and to calculate and correctregister error. FIG. 2 gives a block diagram for the complete process.It starts with general housekeeping routines (#100) in the CPU. WhenEncoder Control Board gives a trigger signal for a specific web surface,the strobe light illuminates the web for a fraction of a second with ahigh intensity light burst. The Frame Grabber Board (#102) stores thenext complete frame image from the camera image in the memory, to besubsequently used by CPU for further analysis. When Frame Grabbercompletes storing the image, it registers this event with the CPU. TheCPU constantly monitors events registered by Frame Grabbers. If an ImageAcquired event is registered from a Frame Grabber, CPU starts analyzingthe image to locate blobs (#104) in the image memory of the FrameGrabber. Once all blobs are tagged, they are qualified (#106) aspotential register marks.

FIG. 2A gives a block diagram of the “Qualify Marks” procedure (#106,#200). This process begins with initialization of blob number (#202).Width of each blob is calculated (#204) and it is confirmed to be withinallowable range (#206). If the width is out of allowable range, the blobis rejected as a potential mark and next blob is analyzed (#214).Similarly, height of each blob is calculated (#208) and it is confirmedto be within allowable range (#210). If the height is out of allowablerange, the blob is rejected as a potential mark. Once both conditionsare satisfied, the blob is tagged as a qualified mark (#212). Thisprocedure is performed for each blob in the image.

Subsequent to the “Qualify Marks” procedure, the “Identify Marks”procedure (#108, #300) of FIG. 2B is performed on each qualified mark toidentify the mark pattern. The procedure begins with initializing marknumber (#302). First the mark is checked if it is a qualified mark(#304). If the mark is not qualified then next mark is analyzed (#312).In order to identify the mark patterns, lobes around each mark areidentified first (#306, #500). Referring to FIG. 2C, the “IdentifyLobes” procedure (#306, #500) is performed as follows: the first step isto initialize lobe number. The CPU checks the specific mark for presenceof the lobe (#504) by analyzing color value at the pre-defined lobelocation. If the lobe is present, it is tagged to the mark (#506). Lobenumber is then incremented (#508) to analyze next lobe location. Thisprocedure is continued until all pre-defined lobe locations are analyzed(#510).

When all lobe locations are identified around all qualified marks, thelobe pattern of each mark is compared (#308) with standard patternsdefined earlier. If the pre-defined register mark lobe pattern from aprint cylinder matches with the lobe pattern of an identified registermark then the mark is tagged (#310) with the print cylinderidentification number. indicating that the specific mark was identifiedto be printed by a matched print cylinder. The mark number is thenincremented (#312) to analyze next mark. This procedure is performed forall qualified marks (#314).

For each register mark cluster, a register mark with a unique pattern isdefined as the master register mark (#80). When all register marks in animage are identified, the following filtering procedure (#110, #400) isperformed to filter erroneous marks detected in the above process.

Referring to FIG. 2D, the “Filter Marks” procedure (#10, #400) startswith getting the position (#402) of the master register mark (#80) inthe image. Considering ideal location of all register marks in acluster, including the master register mark, coordinates of the regionof interest are established based on the identified location of themaster register mark (#404). Next step is to initialize the mark number(#406). This mark is checked for identification tag (#408). If the markis not tagged as an identified mark from the “Identify Marks” procedure(#300), then the next mark is analyzed (#414). If the mark is tagged asan identified mark, it is checked to see if this mark is withincoordinates of region of interest (#410). If the mark is outside ofregion of interest boundary, the identifying tag of the mark is removedand it is rejected (#412). If the mark is within region of interestboundary, identification tag is not changed and next mark is analyzed(#414). This procedure is continued for all identified marks.(#416).

Each surface of web also has a Master Print Cylinder. The Master PrintCylinder on each surface is locked and it does not move during automaticregister error correction. Both Lateral and Circumferential registererrors (#116) for print cylinders printing on a surface, are calculatedbased on the Lateral and Circumferential distance (#112, #114)calculated between the register mark, identified by the print cylindernumber and the Master Print Cylinder Register Mark. Register correctionmotors are activated (#118) to correct the register error.

If the Master Register Mark (#80) for a surface is identified in theacquired image, the location of the Master Register Mark (#80) iscompared with the ideal location range to maintain register mark clusterwithin field of view. If Master Register Mark (#80) is out of acceptablerange in lateral direction, AC synchronous motor (#620) is activated tomove the imaging assembly to bring the Master Register Mark withinacceptable range. If Master Register Mark (#80) is out of acceptablerange in circumferential direction the preset count in Encoder ControlBoard (#704) is adjusted to move the location of strobe illumination tobring the Master Register Mark within acceptable range. If the MasterRegister Mark for a surface is not identified in the acquired image fora predefined number of image acquisitions, the control switches to thesearch mode. In this mode, the control starts searching for the registermark cluster in the neighborhood of the last successful identificationof the Master Register Mark. This is achieved by moving the cameramodule for the surface and scanning the circumferential neighborhood b)indexing the location of image along the running direction of the web.When the Master Register Mark is successfully identified in an acquiredimage, the control suspends the search mode and resumes its automaticoperation for that specific surface.

The above mentioned procedure is performed each time an image isacquired from a web surface. If the register mark corresponding to aprint cylinder is identified successfully, the status circle (#824) nextto the cylinder on the operator interface turns green. If the registermark is not identified successfully, the status circle turns red.

Also, for each image analyzed, the lateral and circumferential locationof master register mark is stored. This information is continuously usedto keep the mark cluster within the field of view of the camera. If themaster register mark location deviates from its ideal location,corresponding camera module is moved in appropriate direction andcorresponding encoder preset value is changed appropriately so as tokeep the master register mark within certain allowable area from itsideal location.

To lock a surface in Automatic register correction mode, the operatorselects the surface (s) from the screen and touches the Auto button(#914). At this point the operator has three choices. Selection of firstchoice identifies all register marks on a surface and moves printcylinders to the IDEAL register relation between all print cylinder andmaster print cylinder. Selection of second choice identifies allregister marks on a surface and maintains the CURRENT scanned locationfor register marks from all print cylinders printing on that surface.Selection of third choice brings register marks to a positionrelationship according to the LAST job run.

Once a web surface is locked in automatic mode, the operator can selecta surface and touch a motor enable/disable key (#916) to disable allregister motor movement for print cylinders printing on the selectedsurface. The status circle (#824) next to the cylinder printing on theselected surface on the operator interface turns yellow. To resumeautomatic register correction motor movements, operator selects thesurface currently with disabled motors and then touches the motorenable/disable key.

Operator can also select a print cylinder, which is already locked inautomatic mode, and touch Manual button to change status of the selectedprint cylinder to Manual Override mode. The status circle (#824) on theoperator interface next to the selected cylinder turns blinking yellow.In this mode, the control does not perform automatic registercorrections. Operator can make register corrections manually byselecting the print cylinder and then entering the amount of movementfrom the touch keypad, followed by the direction of required movement(See FIG. 5A and accompanying description).

The operator can access camera view window by touching the View button(#886) followed by selecting a surface. This opens a window (See FIG.5D) on the interface screen to display the exact image acquired by thecamera for the selected surface.

Operator can access Statistical Quality Monitoring screen by touchingappropriate button (#884) on the screen. The window (FIG. 5C) on thescreen graphically shows the register errors for last batch of samples.The sample size is user defined by parameters. To view the registererrors detected for last batch of samples, operator selects a printcylinder, followed by selecting the error direction (lateral orcircumferential). Statistical results of extreme error, mean error andstandard deviation are also displayed in the window, giving accurateidea about consistency of the register quality of the last batch ofsamples for the selected print cylinder.

A Panic Button (#850) is provided and active all times on the touchscreen interface. When this button is touched, any surface locked inautomatic mode is switched to manual mode and all register motoroperations are suspended.

All job setups performed by the operator can be saved with user definedfile names, inputted to the system using keyboard window on touchscreen. The number of job files is restricted by size of the magneticstorage media like Hard Disk Drive or Floppy Drive. Stored jobs can beselected and loaded back in memory at a later date, minimizing job setuptime and waste for similar and repeat jobs.

All parameters in the control are multi-level password protected. Thecontrol is equipped with programmable activation speed, under which theautomatic register motor movements are disabled. After the controlreceives a signal from printing equipment indicating starting ofprinting process, the control waits for a programmable delay. specifiedin impressions, before resuming automatic operations. Correction ratesfor lateral and circumferential directions are also separatelyprogrammable for manual and automatic modes.

The apparatus for scanning the image from the web (#650) is shown inFIG. 3A. It consists of two frames (#600). A web lead-in roller (#602)is provided to accept web (#650) from a previous process equipment. Aweb lead-out roller (#604) is provided to deliver the web to the nextprocess equipment on the printing line. Between lead-in and lead-outrollers, the web travels over two rollers (#606, #608). The imagingassembly consisting of a CCD camera and a strobe light (#610) scans thetop side of the web passing over roller (#606). The imaging assemblyconsisting of a CCD camera and a strobe light (#612) scans the bottomside of the web passing under roller (#608). Both imaging assemblies(#610, #612) are mounted on a carriage (#614), which moves and positionsthe camera modules at an operator specified location across web width.The carriage (#614) is equipped with v-groove guide wheels and the guidewheels keep the camera on the guide (#616). The carriage is alsoequipped with an AC Synchronous Motor (#620) and a timing belt pulley. Atiming belt (#618) is provided across the width of the carriage guide.Rotation of the motor (#620) on the carriage moves the carriage (#614),motor (#620) and imaging assembly (#612, #614) across the web. Carriageguide is mounted on the mounting brackets (#622), which is subsequentlymounted on the frames (#600).

FIG. 4 is a block diagram giving general arrangement of differentcomponents of the control. The main processor of the control is an IntelPentium Micro-processor based Personal Computer (#700) with ISA and/orPCI expansion slots. In addition to the standard components of apersonal computer, like power supply, video display card, hard drive,motherboard and related electronics, the control utilizes onecommercially available Frame Grabber Board (#702), like Data TranslationDT55, for each surface to be monitored. One Encoder Control Board (#704)is inserted in the PC expansion slot. One commercially availableencoder, like Dynapar HA625, is used to monitor drive shaft position ofthe printing apparatus. The system also consists of an imaging assemblyconsisting of commercially available CCD camera (#708), like HitachiKP-M1, and a commercially available Strobe Light (#710), like EG&GMVS-4000.

Encoder Control Board accepts two channels of pulses and a channel ofreset pulse from an encoder (#714) through cable (#716). The encoder isdriven from a drive shaft of the printing press. The encoder iscommercially available from various sources like Dynapar. All Encoderchannels carry a complimentary signal for noise immunity. Two channelsof pulses from encoder are in quadrature, at 90 degree out of phase. Theencoder control board consists of quadrature decoding circuit to get acount on each rising and falling pulse of both encoder channels. Thereset pulse channel gives one reset pulse for every revolution, whichresets the counts in encoder control board. Based on circumferentiallocation of the image (#712) set by the control operator, a number ispassed from the personal computer to the encoder control board. EncoderControl Board continuously monitors the count from an encoder, and thusit monitors the position of the drive shaft which is also the positionof the print. When the count in the encoder control board is equal tothe count preset by personal computer, the encoder control board gives atrigger signal to the associated Frame Grabber (#702) through cable(#720) and the associated Strobe (#710), through cable (#722), in thecorresponding imaging assembly (#706). In response to the trigger signalfrom the encoder control board, the strobe emits intense and a veryshort burst of light. Since camera (#708), like Hitachi KP-M1, in theimaging assembly is run in continuous mode, the strobed image of thesurface under camera is acquired in the camera. The camera has built-insynchronizing circuits to generate video synchronization signals. Thetrigger signal from the encoder control board also gives a signal to theFrame Grabber to store the next complete frame of image from the camerathrough cable (#718). When Frame Grabber has finished storing the image,it sets an internal flag to indicate that it has a new image stored.Personal Computer constantly monitors the status of this flag. If a newframe of image is received, the CPU analyzes it. After analysis iscompleted, the CPU resets the flag in the Frame Grabber. The FrameGrabber acquire a new frame of image only if the flag is in resetcondition.

The encoder control board consists of up to four count and comparecircuits for up to four surfaces to be monitored by the control. Theabove mentioned procedure for image acquisition is applied to all thesurfaces monitored by the control.

It will be understood that the embodiments described herein are merelyexemplary and that a person skilled in the art may make many variationsand modifications without departing from the spirit and scope of theinvention. All such modifications and variations are intended to beincluded within the scope of the invention as described herein.

What is claimed is:
 1. Apparatus for identifying each register mark in aregister mark cluster in a multi-color automatic registration system,including a plurality of register marks, a respective one of saidregister marks printed on a surface by a corresponding one of aplurality of print cylinders, said apparatus comprising: each of saidregister marks having a geometrically unique shape different from theremaining ones of said register marks including each having a uniquelydifferent, visually apparent, perimeter profile, each of said registermarks, when a predetermined registration is achieved, printed at aseparate, respective position on said surface which is neitherco-extensive with or overlapping of the respective positions of any oneof said other register marks; means for locating each possible registermark and for determining position and size information for each possibleregister mark; means for identifying the geometrically unique shape ofeach register mark; means for identifying a region of interest on saidsurface; and, means for correlating the geometrically unique shape ofeach register mark with pre-defined shapes assigned to different printcylinders printing on the surface, whereby close registration betweencolors printed on the surface by said plurality of print cylinders ismaintained.
 2. The apparatus of claim 1 wherein the register markcluster comprises a pattern in which each mark is geometrically uniqueand associated with a different print cylinder.
 3. The apparatus ofclaim 1 wherein the means for locating a possible register markcomprises means for determining position coordinates and means forqualifying each possible register mark.
 4. The apparatus of claim 3wherein the means for qualifying each register mark includes means fordetermining height and width of each register mark and comparing it withan allowable range of height and width respectively.
 5. The apparatus ofclaim 1 wherein each said register mark includes at least one lobe, saidmeans for identifying shape of each register mark includes means foridentifying number and location of lobes present on each said registermark.
 6. The apparatus of claim 1 wherein said means for identifyingregion of interest includes means for identifying a master register markwith a pre-defined shape on the surface and defining a region ofinterest based on coordinates of said master register mark and means offiltering register marks.
 7. The apparatus of claim 6 further includingmeans of filtering register marks including means for comparing positioncoordinates of each register mark with the coordinates of said region ofinterest and rejecting marks outside of said region of interest aspossible register marks.
 8. The apparatus of claim 1 wherein said meansfor correlating shape of each register mark with pre-defined shapesincludes means for comparing a lobe pattern of each register mark withpre-defined lobe patterns assigned to each printing cylinder and tagginga respective print cylinder lobe pattern identification to each saidregister mark.
 9. A method of identifying color to color register marksprinted on a moving web comprising a plurality of geometrically uniqueregister marks in a multi-color automatic registration system, themethod comprising the steps of: providing each of said register markswith a geometrically unique shape different from the remaining ones ofsaid register marks including each having a uniquely different, visuallyapparent, perimeter profile; printing each of said register marks, whena predetermined registration is achieved, at a separate, respectiveposition on said surface which is neither co-extensive with oroverlapping of the respective positions of any one of said otherregister marks; acquiring an image of a moving web; locating all blobsin the acquired image, each of said blobs having a respective width andheight; qualifying each of said blobs by assuring that a respective blobwidth is within an allowable width range and a respective blob height iswithin an allowable height range; identifying possible register marks byidentifying a geometrically unique shape of each possible register mark;identifying a master register mark and defining a region of interestbased on coordinates of said master register mark; and rejectingpossible register marks outside of said region of interest.
 10. Themethod of claim 9 wherein an acceptable register mark includes at leastone lobe, the step of identifying the geometrically unique shape of eachregister mark comprises identifying the number and location of lobespresent on each register mark.
 11. The method of claim 9 wherein thestep of identifying a master register mark, wherein an acceptable masterregister mark includes at least one lobe, comprises comparing the numberand location of lobes of a register mark with a pre-defined lobe patternfor a master register mark.
 12. Apparatus for providing a trigger signalof a short duration for illuminating a moving printed web at a specificlocation and for acquiring an image of the illuminated moving printedweb, comprising: means for identifying a location of the moving printedweb including an encoder, said encoder driven synchronously to the printcylinders said encoder including an encoder control board comprising ofa plurality of counters to count the pulses from said encoder and tocompare the count accumulated in the counters with a preset positioncount for said predetermined location on the moving printed web; meansfor comparing said location of the moving printed web with apredetermined location on said printed web; and means for providing atrigger signal at said predetermined location, wherein said means forproviding a trigger signal comprises an output circuit to provide atrigger signal of predetermined short duration, when said accumulatedcount by said encoder control board is equal to the preset positioncount, whereby said moving printed web is illuminated at the beginningof the trigger signal and the image acquired at the end of the triggersignal.
 13. Apparatus for maintaining a register mark cluster, includinga plurality of register marks, in a field of view across and along aprinted web of an automatic color to color register system for aprinting press employing a plurality of print cylinders, comprising:each of said register marks having a geometrically unique shapedifferent from the remaining ones of said register marks including eachhaving a uniquely different, visually apparent, perimeter profile, eachof said register marks, when a predetermined registration is achieved,printed at a separate, respective position on said web which is neitherco-extensive with or overlapping of the respective positions of any oneof said other register marks, each of said register marks associatedwith a different one of said print cylinders; means for locating eachpossible register mark and for determining position and size informationfor each possible register mark; means for identifying a respectiveshape of each possible register mark; means for identifying a masterregister mark; means for maintaining said master register mark in alateral direction across a specified area within said field of view;and, means for maintaining said master register mark, in acircumferential direction along said specified urea within said field ofview.
 14. The apparatus of claim 13 wherein the means for locating eachpossible register mark comprises means for determining positioncoordinates and means for qualifying each possible register mark. 15.The apparatus of claim 14 wherein the means for qualifying each possibleregister mark comprises means for determining height and width of eachpossible register mark and comparing it with an allowable range ofheight and width respectively.
 16. The apparatus of claim 13 wherein anidentified register mark must include at least one lobe, said means foridentifying a respective shape of each possible register mark comprisesmeans for identifying the number and location of lobes present on aregister mark.
 17. The apparatus of claim 13 wherein an identifiedregister mark must include at least one lobe, said means for identifyinga master register mark comprises means for comparing the number andlocation of lobes of a possible register mark with a pre-defined lobepattern as to number and location for a master register mark.
 18. Theapparatus of claim 13 wherein said means for maintaining said masterregister mark within said specified area comprises means for moving animaging assembly across the web, based on said master register marklocation, in a lateral direction.
 19. The apparatus of claim 13 whereinmeans for maintaining said master register mark within said specifiedarea b comprises means for adjusting a preset count on an encodercontrol board, based on the master register mark location in acircumferential direction.